Recently, significant advances have been made in the production of polyurethane elastomers. Rapid processing times of three minutes or less are known to be obtainable by simultaneously reacting and forming polyurethane elastomer formulations using a process such as, for example, the Reaction Injection Molding (RIM) process, to produce cellular or solid elastomers. Since the "in-mold" time for a process such as RIM is small compared to that for conventional casting technology, curing of the elastomer is generally incomplete at the time of separation of the elastomer from the mold ("demolding") when conventional organotin catalysts (e.g., dibutyltin dilaurate) are employed in typical catalytic amounts. Attempts to increase the catalyst loading of conventional catalysts in order to provide faster curing result in a mold filling problem since higher conventional catalyst levels cause premature gelation of the reaction mixture.
Certain organotin catalysts are known as "delayed action" catalysts inasmuch as they provide delayed catalysis of a polyurethane reaction mixture. By way of illustration, such catalysts are described for use inter alia in the RIM process in the following trade literature references: (a) "Additives for Plastics-Polyurethane Catalysts", Plastics Engineering, March 1977, pp. 39-42; and (b) "Urethane Catalysis: Trimer Foams Spur R&D", Plastic Technology, July 1976, pp. 67-70. Delayed action organotin and organomercurial catalysts are described as suitable in the RIM process when used in conjunction with an amine co-catalyst in "Urethane Catalysts: Focus on Delayed Action", Plastics Technology, July 1977, pp. 117-120.
It has now been found that a process employing higher-than-normal amounts of a particular delayed-action organotin catalyst, namely dialkyltin dimercaptide carboxylic acid ester, in a process such as RIM provides process advantages in the production of solid and microcellular polyether polyurethane elastomers. First, the increased loading of dialkyltin dimercaptide carboxylic acid ester makes it possible to avoid the necessity of employing expensive amine catalysts. Second, there is no mold filling problem in view of the delayed action property of dialkyltin dimercaptide carboxylic acid ester. Third, the resulting elastomers exhibit enhanced "green strength" (cracking resistance) upon demolding.